That tie. He just won't take it off, even when picking his way in sweltering heat through the rubble left by Hurricane Irma on the French Caribbean island of St Martin.

President Emmanuel Macron has shaken French politics to its core but dares not breach the dress code for a French chief of state.

The tie, preferably dark, is de rigueur.

King Willem-Alexander of the Netherlands also flew to St. Martin to assess damage and display royal solidarity on the Dutch half of the island. He wore a khaki-colored shirt, sleeves rolled to the elbows - and no necktie.

"He's a real king. He doesn't need to post signs to show his stature," said Jamil Dakhlia, a Sorbonne University sociologist specializing in political communications.

The French Revolution ended the country's monarchy in 1789. The French presidency remains powerful but there is "a need to show with symbols one's legitimacy. So, you must keep the tie on," Dakhlia explained.

The Dutch king also is not a 39-year-old former investment banker looking to upset the political system with his upstart centrist party and planning to undo France's nearly sacrosanct labor laws - all while sliding in popularity.

Conscious of his baggage, Macron donned a tie while campaigning and has kept it on ever since, even during events in which sartorial elegance might be understandably cast aside.

There he was in April, before his May election, in a coat and tie trying to talk down screaming angry factory workers outside their Whirlpool plant.

Two months later, as president, he was playing tennis sans vest but with a tie from a wheelchair alongside disabled athletes to promote Paris' bid to host the 2024 Olympics. The French capital went on to win the opportunity.

On Monday, Macron, doubtless wearing a thin dark tie, will attend his first U.N. General Assembly in New York. There he will also meet with President Donald Trump, who is known to have a penchant for long neckties, often red or blue.

In St Martin for two days, the French president trudged through debris on the devastated island wearing a dark tie over a white shirt, the sleeves rolled up in the smothering heat and humidity but mysteriously always crisp-looking.

"What surprised me the most was that he took off his suit jacket," said Dakhlia.

"For a long time ... (Macron) was accused of not having legitimacy, of being too young, with no real political capital," Dakhlia noted, saying Macron would have removed his tie at his peril. "If he had done it ... It would have been noted as a way to try to be close to the people, as insincere stagecraft."

The Western neck tie is widely considered to have its origins with 17th-century Croatian mercenaries who came to France's aid, wearing colorful neck bands, during the Thirty Years War between European powers. The neck band evolved and spread.

Today, the wardrobe of French leaders, tie included, is scrutinised by journalists deciphering the strengths and weaknesses of their chiefs of state. Macron's ties have grown darker and thinner as president and the knots he used to use in his banking days have changed.

Macron may have taken a clue from his unpopular predecessor, Francois Hollande, who had endless bad tie days. Hollande's cravat was always crooked and he became the butt of jokes.

A website was even started, francois-tacravate.Fr, which graded the appearance of Hollande's ties on each public outing.

But even as a rookie president, Hollande knew the French dress code. He was the only world leader at a 2012 G-8 summit at Camp David, just after his election, to show up wearing a necktie.

"Francois, we said you could take off the tie," the host, former President Barack Obama, joked.

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